A shackle is attached to the floor in this April 2005 file photo of an interview room at the U.S. detention facility in Guantanamo Bay, Cuba.

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Sleep-deprived people are almost five times more likely to sign false confessions, according to a new study, adding to a growing body of psychological research that suggests our memories are less reliable than previously assumed, with complex consequences for the criminal justice system's use of eyewitness' and suspects' accounts.

A research team led by Kimberly M. Fenn, an associate professor of psychology at Michigan State University, put subjects through a series of logic puzzles and computer exercises, during which they were warned not to press the "escape" button or risk losing important data. Subjects were then monitored as they either slept in the lab or were kept awake all night, and then asked in the morning to sign a document summarizing their experience. The statement each person was asked to approve inaccurately said that he or she had pushed the "escape" key.

Subjects who initially refused to sign were encouraged to do so. After two requests, 38.6 percent of people who had slept eight hours the night before signed the false confession, versus 68.2 percent of those awake for 24 hours. Those who rated their sleepiness as a 6 or 7 on the 7-point Stanford Sleepiness Scale, however, were 4.5 times more likely to sign than those who had a good night's sleep. Subjects were also more likely to falsely confess if they had scored lower on an intelligence test or if they displayed an impulsive problem-solving style on the logic puzzles.

"We propose that sleep deprivation sets the stage for a false confession by impairing complex decision making abilities — specifically, the ability to anticipate risks and consequences, inhibit behavioral impulses, and resist suggestive influences," the authors write in the Proceedings of the National Academy of Sciences.

"A false admission of wrongdoing can have disastrous consequences in a legal system already fraught with miscarriages of justice," they write, proposing that suspects be given a sleepiness assessment before undergoing interrogation, and that all interrogations be videotaped so that judges, lawyers and jurors can assess the context of a confession for themselves. Although sleep-deprivation may not be police's intent, the authors point out that hours-long interrogations, or ones that take place overnight, could induce the same confusion and increased chances of a false confession.

In a 2014 study led by Samuel R. Gross, a professor at the University of Michigan School of Law, researchers made a "conservative estimate" that at least 4.1 percent of death sentences arise from false convictions. Dr. Fenn's team writes that 15 to 25 percent of false convictions hinge on false confessions, which often influence jurors even when they've been told that the confession was coerced.

Sleep deprivation impairs "a whole host of cognitive operations," and may reduce "inhibitory control, leading people to make riskier decisions, and [interfere] with their ability to anticipate and measure the consequences of their actions," Fenn's team writes.

But even under less severe conditions, researchers say that sleep-deprived people may be more susceptible to "suggested" memories, and confusing the source of their memories, such as mistaking something they've read for an event they experienced first-hand.

Although the Fenn team says it is important to guard against false confessions, it also acknowledges important caveats to the study. For instance, subjects did not know what consequences they would face for signing or not signing the false confession, unlike a criminal suspect.

The also emphasize that their research does not touch on whether sleep deprivation affects true confessions:

If sleep deprivation increases both true and false confessions, then law enforcement and military personnel may want to carefully weight the costs and benefits of sleep deprivation in an interrogation, particularly when collecting intelligence that could prevent the loss of innocent lives. Future research would do well to examine the role of sleep deprivation on both true and false confessions.